The lengths of the segments AB equal to 14 cm, BC equal to 6 cm, AD equal to 21 cm, and DE are related

The lengths of the segments AB equal to 14 cm, BC equal to 6 cm, AD equal to 21 cm, and DE are related by the proportion AB: AD = BC: DE. Find the length of the line segment DE.

Let us briefly write down the condition of the problem:
AB = 14 cm;
AD = 21 cm;
BC = 6 cm;
DE -? cm.
Let’s write down the proportion and substitute numerical values into it:
14: 21 = 6: DE.
Let’s solve this proportion:
DE = 6 * 21: 14 = 126: 14 = 9 cm length DE
Answer: The length of the DE segment is 9 centimeters.